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Oswald
Registered: Apr 2002
Posts: 5086 |
VIC and the odd/even fields
okay this is getting confusing for me now. in another thread on lemon64 groepaz says that the vic does always display the same field, but it doesnt matter if its odd or even, and it lights up both the odd/even lines.
some1 can tell me:
- does vic use odd or even or dontcare lines?
- what does the term field mean from the tv electronics viewpoint?
- how does the vic only light up the odd (forex.) lines on the tv screen, and a little bit from the other ones?
- are there really 2 modes in the tv electronics for odd / even fields
- why does computer graphics flicker a hell more lot while "normal" tv screens looks as steady as my ass?
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Nightlord
Account closed
Registered: Jan 2003
Posts: 131 |
ok I have a question. I see a contradiction between what Groepaz says and what Magervalp says about Chrominance being half resolution.
So there are 576/2= 288 scan lines in one frame (between 2 v-syncs). For each 288 scanlines, The corresponding part of the signal starts with h-sync, then color burst, then video_info. My understanding was that the low freq amplitude of video_info is luminance and the color gets modulated and added to the signal in a higher freq smaller amplitude sinusoidal whose amplitude determinas "saturation" and whose phase determines "hue".
From what I understand, Groepaz is saying there are 288/2=144 lines in each frame that has this modulated color info and 2 consecutive scanlines in same frame use the same crominance.
Where as Magervalp refers to "horizontal resolution being half". thus two "pixels" (thinking of pixel as a part of crt tube where the beam covers in 1/50/288/720 seconds) next to each other share the same chrominance but can have different luminances. This way all 288 scan lines in a frame has different color info modulated in them.
Do I understand you guys correctly? If yes which is true? I was thinking Magervalp's statement is true, but I am not 100% sure
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chatGPZ
Registered: Dec 2001
Posts: 11360 |
chromincance has lower resolution in both dimensions :) in X its valid for more than one pixel, in Y it "drains" down the display due to the delay line. |
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Nightlord
Account closed
Registered: Jan 2003
Posts: 131 |
ok so all 288 lines between 2 v-syncs have different chrominance, right?
The "draining" you refer to confuses me though... Isn't that true for Y as well? |
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chatGPZ
Registered: Dec 2001
Posts: 11360 |
Quote:ok so all 288 lines between 2 v-syncs have different chrominance, right?
yes
Quote:The "draining" you refer to confuses me though... Isn't that true for Y as well?
no, thats only done for chrominance (and only on PAL *afaik* - ntsc works a bit different). |
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White Flame
Registered: Sep 2002
Posts: 136 |
The vertical color blending on PAL is actually due to hardware on the display deliberately performing the blend, not due to the signal itself, right?
And this might help or hinder the discussion: http://www.white-flame.com/interlace.gif
and the whole "half horizontal color resolution" thing is more about bandwidth than digital resolution. The signal can only change so sharply due to frequency limitation. So you can _start_ a color change anywhere on the analog line, but it's limited to how fast it can change. The luminance signal can change much more rapidly, thus has a finer resolution. |
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chatGPZ
Registered: Dec 2001
Posts: 11360 |
Quote:The vertical color blending on PAL is actually due to hardware on the display deliberately performing the blend, not due to the signal itself, right?
yep
Quote:And this might help or hinder the discussion: http://www.white-flame.com/interlace.gif
makes sense to me :) |
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Oswald
Registered: Apr 2002
Posts: 5086 |
whiteflames illustration makes sense even for me, but is again source of confusion.
according to jackesser this happens:
_e
ov
de
dn
10
12
32
34
54
56
76
78
now is there an "empty" scanline between consecutive odd / even scanlines or not ?!
or: is one scanline "doubled" in height according to the above ascii art, and the vertical resolution only "doubles" by having an "half" scanline shift between odd/even frames?! |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: whiteflames illustration makes sense even for me, but is again source of confusion.
according to jackesser this happens:
_e
ov
de
dn
10
12
32
34
54
56
76
78
now is there an "empty" scanline between consecutive odd / even scanlines or not ?!
or: is one scanline "doubled" in height according to the above ascii art, and the vertical resolution only "doubles" by having an "half" scanline shift between odd/even frames?!
"is one scanline "doubled" in height according to the above ascii art, and the vertical resolution only "doubles" by having an "half" scanline shift between odd/even frames?!"
BINGO! |
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Oswald
Registered: Apr 2002
Posts: 5086 |
jack, wont work if I take into consideration that the "half scanline shift" happens due to having "half screen wide" scanlines. :P o_O |
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MagerValp
Registered: Dec 2001
Posts: 1074 |
Quote: keep me out of that kthxbye :)
*sigh*
Here's another experiment for you:
Connect a C64 to a 1084 mounted on a table that has an adjustable height. Adjust the 1084 so that every VIC scanline is exactly 1 mm high. Now simultaneously display a 0.5 pixel upscroller, and move the table down at a constant speed of 25 mm per second. In what was does this display differ from that of an interlaced Amiga display (assuming a 1084 with infinite height, etc)?
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